Delayed feathering in chickens

Contrarily, sex-linked delayed-feathering is very frequent, particularly in meat-type breeds like Brahma, Cornish, Cochin, Rhode Island Red, Wyandotte, Plymouth Rock and Orpington.

Sex-linked genetic variation has proven to be very useful for the sex identification of one-day-old chicks in commercial hybrids.

Sex-linked feathering is controlled by locus K on the sexual chromosome, with four known alleles in the following dominance order: Kn > Ks > K > k+.

One-day-old chicks lack primary and secondary remiges (they may appear as extremely small pinfeathers, but always shorter than the coverlets).

[7] When fast normal-feathering k+k+ cocks are mated to delayed-feathering K hens, the sex of all the descendants can be easily recognized at hatch: resulting female chicks k+ have fast normal-feathering (see Figure 2A) while male chicks Kk+ have delayed-feathering (see Figure 2B and 2C).

Through controlled matings and selection, K gene was put into egg-type breeds like White Leghorn, where sex-linked delayed feathering did not originally occur, thus obtaining genetically delayed-feathering female parent breeders to be mated with fast normal-feathering male parent breeders in order to obtain sexable female chicks of the fast normal-feathering type.

In meat-type breeds, feather sexing was not so extended to commercial broiler production because resulting poorly-feathered males are very prone to scratches in the skin of the belly, which can discredit carcass quality.

The preparation of new breeds to produce feather sexable crosses implies considerable previous genetic work which is completely beyond the means of most poultry farmers.

[7][12] That is, one-day-old chicks with primary remiges shorter than coverlets carry the K gene of sex-linked delayed-feathering (see Figure 2C).

"Retarded" chicks show the first three or four primary remiges of normal length, with each new feather being shorter than the preceding one (see Figure 3B).

At ten days of age they still lack rectrices and show small or no development of secondary remiges (see Figure 3C).

Figure 1. Feathering types in ten-day-old chicks . Left: Fast normal-feathering chick. Right: Delayed-feathering chick carrying sex-linked K gene
Figure 2. Feathering types Diagram of the wing of a one-day-old chick in dorsal view: A fast normal-feathering with the primary remiges (1a) longer than the coverlets (2a). B sex-linked delayed-feathering with the primary remiges (1a) of the same length than the coverlets (2a). C modified delayed-feathering with the primary remiges. (1a) shorter than the coverlets (2a).
Figure 3. Effect of autosomal genes of T series on 10-day-old chicks.
(A) Normal-feathering, with a T − genotype. (B) "Retarded"-feathering, with t s t s genotype. (C) "Tardy"-feathering, with tt genotype.